Halogenation of saturated hydrocarbons



Jan. 30, 1945. J. c. SCHILLER 2,368,495

HALOGENATION OF SATURATED HYDROCARBONS Filed Sept. 5, 1942 INVE OR.

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enemas he. so, tees err rare gar naaocanarron or sarnaa'ran nrnaocons .liames C. Sober, Eaytown, Tex, assignor to Standard (ill Development Company, a coration of Delaware Application September 5, 1942, Serial No. 457,388

Claims. (in. ace-16s) served in order to direct the halogenation of a saturated hydrocarbon toward the desired end product or products. Experience has indicated that the reaction is sensitive to many disturbing factors and that therefore the entire combination of operating conditions must be maintained in a certain critical, relation to each other.

Briefly, according to the present invention, the essential requirements for successful halogenation of a saturated hydrocarbon are that the starting material should be substantially pure or at least 90 per cent pure, that the operating temperature should be maintained at a low level not in excess of about 45 0., preferably between about 20 and about C., that water should be excluded from the reaction zone, that the hydrocarbon should be present in the reaction zone in excess of the halogen and that the reaction mixture should be continuously under the influence of light, preferably predominantly blue or ultra violet.

Another feature of the present invention resides in the discovery that the course of reaction between the halogen and a saturated hydrocarbon capable of yielding a'number of derivatives can be directed so as to prodtrce a product which is predominantly the dihalide by incorporating in the reaction-mixture a promoter of the type exemplified by nitro-aromatics. It is preferred to use a nitro-aromatic, such as nitro-benzene, which is liquid and miscible with the reaction mixture. The promoter is used in very small amounts, generally not more than a fraction of a percent of the hydrocarbon.

The manner in which the process 'of the present invention is carried out will be clearly understood from the following detailed description of the accompanying drawing in which the single figure is a front elevation in diagrammatic form of one type of apparatus which may be employed for the performance of the process,

Referring to the drawing in detail, numeral I designates a feed line for the hydrocarbon to be. halogenated. This feed line empties into an incorporator 2. Ahead of the incorportor is a I branch line' 3 through which the halogen is introduced into the hydrocarbon; The two lines will be provided with valves and, preferably, witha type of proportioning device common in the art for automatically regulating the proportions in which the two substances are mixed. After being thoroughly mixed in the reaction chamber, the mixture is passed through a transparent vessel or pipe El adjacent to which are arranged one or more lights 5 for maintaining the desired light intensity in the reaction mixture. In order to control the reaction temperature and keep it within the desired limits a cooling coil 6 is arranged in the pipe 4 for/carrying a stream of cooling medium, such as ice water. A

The reaction mixture leaving the reaction zone is discharged into a fractionating column 1 from which one or more halogen derivatives may be withdrawn either as a mixture from the bottom through line 8 or as separate streams from different points along the column. The unreacted hydrocarbon and the hydrogen halide resulting from the reaction leave the fractionating column I through line 9 and are fed into asecond fractionator Ill at an intermediate point thereof from the top of which the hydrogen halide is discharged-through line Ii and from the bottom of which the unreacted hydrocarbon is conducted through line l2 back to the charge feed line so as to insure the maintenance of an excess of hydrocarbon in the system.

. The hydrocarbon introduced into line I can, as previously indicated, he a saturated open chain or cyclic hydrocarbon. The process of the present invention is more advantageously applicable to hydrocarbons having 4, 5, or 6 carbon atoms. The hydrocarbons of lower molecular weight do not possess the isomers which create some of the problems to the solution or avoidance of which the method of the present invention is directed.

It has been previously mentioned that in the reaction it" is preferred to maintain an excess of hydrocarbon. The amount of excess will depend upon the type of halide derivative desired for the production of the amount of halide. The molecular ratio between the hydrocarbon and the halogen is preferably of the order of at least 5:1. This ratio can be increased if desired. In order to direct the reaction toward a dihalide, the above ratio is reduced but should preferably be maintained in excess of 3:1. In order to .favor the production of-higher halides, theaforementioned ratio is correspondingly reduced but in no case is it reduced to stoichiometrlcal proportions.

In an actual operation according to the present invention a quantity of hydrocarbon material in the pentane boiling range was fractionated carefully in an efficient fractionatlng column with high reflux ratios employed. A' out having a boiling range of 0.2 C. was segregated and used as the material to be halogenated. The halogen employed in this instance was bromine, and it was used in an amount of 0.97 mol in dry condition for each 1.3 mols of the dry pentane fraction. The reaction temperature was maintained at between 28 and 31 C. by cooling with ice water. The reaction mixture was subjected to activation by light from a No. 2 Mazda photo flood lamp. Since this operation was carried out on a batch principle rather than on the continuous principle illustrated inthe drawing, the hydrocarbon was placed in the vessel and the bromine added to it slowly and continuously. At the out-set it'will be appreciated that the molar ratio between the hydrocarbons and the bromine was extremelyhigh. The bromine was permitted to drop into the hydrocarbon at a rate such that the color of the reaction mixture remained a bright cherry red throughout the reaction.

Upon completion of the reaction fractionation ,of the reaction mixture yielded unreacted npentane, a mono-bromide, a dibromide and a tribromide. The yield of brominated material constituted more than 9.0 mol per cent of the theoretical based on the input mols ,of bromine. The bromine derivatives in the order oi their yields were 2-bromopentane 50.2 mol per cent, 2,3-dibromopentane 35.5 mol per cent and 2,3,4- tribromopentane 14.3 mol per cent.

Similar runs under the same conditions were made with 2-methylbutane, Z-methylpentane, nhexane, cyclohexane, and l-bromobutane. The products obtained from each of these starting materials respectively, were:

monohalide, conversion of some monohalide to dihalide takes place and additional hydrocarbon is converted to the monohalide. It might be expected that, since the second carbon atom on a normal paramn chain is most susceptible for halogenation tothe monohalide, the next to the last carbon atom on the other end of the carbon chain would be the next most susceptible for halogenation to form the dihalide. However, I have discovered that further substitution in these cases always takes place On the secondary carbon atom adjacent to that carbon atom on which the first atom of halogen has substituted. This phenomenon of successive substitution on adjacent carbon atoms is quite general as is illustrated by the examples given above.

One of the meritorious features of the present invention is that its advantages are best realized when working with hydrocarbons of molecular weight indicated and it is these particular hydrocarbons which are of great importance in the production 01' raw materials for polymerization processes by which are produced important basic materials such as synthetic rubbers, plastics, lacquers, drying oils, etc. From these halogenated derivatives for example can be produced substances like butadiene, isoprene, dimethylbutadiene, and other diolefins, various acetylene derivatives, alcohols, esters, and other important products, all of which are or great commercial value.

The nature and objects of the present invention having been thus described, and illustrated, what is claimed as new and useful and is desired to be secured by Letters Patent is:

Configuration and mol per cent of products Monobromide Dibromide Tribromide 2-bromo-2-methylbutane, 47.6 2-bromo-2-methylpentane, 55.1 2-bromohexanc, 53.2 1-bromocyclohexane, 7.0

2,3-dibromohexane, 29.4 Lil'dibromocyclohexane, 79.3 1,2-dibromobntane, 63.5

2,3-dibromo-2-methylbutane, 45.8 2,3-dibromo-2-methylpentane, 38.4

2,3,4-tribromo-2-methylbutane, 6.6 2,3,4-tribromo-2-methylpentane, 6.5 2,3,4-tribromohexane, 17.4 1,2,3-tribromocyclohexane, 13.7 1,2,3 tribromobutane, 36.5

It will be observed that the product distribution for 2-methylpentane was 55.1 mol-per cent of monobromide, 38.4 mol per cent of dibromide,

and 6.5 mol per cent of tribromide. When the 50 same bromination was conducted with the addition of 12 cc. of nitrobenzene to the isohexane the distribution of the products became 6.7 mol per" cent of monobromide, 82.7 mol per cent of dibromide, and 10.6 mol per cent of tribromide.

A particularly novel feature of my invention is the discovery that, by employing a relatively pure hydrocarbon feed stock and the preferred halogenation conditions disclosed herein, the halogenation proceeds as a chain reaction and the halogen substitutes on the carbon chain in a predictable, step-wise fashion. When paramn hydrocarbons are employed, either of the straight chain variety or those with terminal branched chains, the first carbon atom on which substitution occurs in always the second carbon atom in the longest carbon chain. 'When reaction between the hydrocarbon and the halogen has reached an equilibrium for the formation or the substantially pure anhydrous state with an an hydrous halogen at a temperature below about C. in the presence of a small amount of a nitro-aromatic and under the influence of light while maintaining in the reaction mixture'an ex- 'cess 01' hydrocarbon.

2. A method according to claim 1 in which the temperature is maintained between 20 and 30 m CI-and the light employed is selected from the blue and ultraviolet bands.

3. A method according to claim 1 in which. the hydrocarbon halogenated is isopentane.

1 in which the 4. A method according to claim hydrocarbonisat least 9 0 pure.

5. Amethodaecordingtoclaim linwhichthe nitro-aromatic is nihobenzene.

James c. SCHILLER. 

